Suppression of the humoral immune response to inactivated Newcastle disease virus by Mycoplasma meleagridis in the Turkey.

Groups of Mycoplasma meleagridis-free and -infected turkeys were vaccinated against Newcastle disease virus (NDV) at 5 and 8 weeks of age. The two groups did not differ significantly in antibody response to NDV as measured by the hemagglutination-inhibition test when a live vaccine (TCND) was used, but the two groups differed significantly when an inactivated vaccine was used; titers were higher in the mycoplasma-free group in both primary and secondary responses. The difference between responses of the mycoplasma-free and -infected groups to inactivated and live NDV was explained by a current hypothesis about the ontogeny of B-cell differentiation in the bursa of Fabricius and by its interference by M. meleagridis.